Liquid crystal display device

ABSTRACT

According to one embodiment, a liquid crystal display device includes a first substrate including a first alignment film covering a pixel electrode, a second substrate including a second alignment film covering a second common electrode, a sealant attaching the first substrate and the second substrate, and a liquid crystal layer held between the first alignment film and the second alignment film, wherein the first alignment film and the second alignment film are formed of a material in which a principal chain is composed of silica (SiO 2 ), and extend at a position overlapping the sealant between an inner face and an outer face of the sealant.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.16/717,575 filed Dec. 17, 2019, which is a continuation of U.S.application Ser. No. 15/895,494 filed Feb. 13, 2018, which is acontinuation of U.S. application Ser. No. 15/203,544 filed Jul. 6, 2016,which is a continuation of U.S. application Ser. No. 14/503,544, filedon Oct. 1, 2014, and is based upon and claims the benefit of priorityfrom Japanese Patent Application No, 2013-206275, filed Oct. 1, 2013,the entire contents of each of which are incorporated herein byreference.

FIELD

Embodiments described herein relate generally to a liquid crystaldisplay device.

BACKGROUND

In recent years, in active-matrix-type liquid crystal display devicesincluding switching elements in respective pixels, a structure mainlyusing a vertical electric field, such as a vertical aligned mode, hasbeen put to practical use. In such a liquid crystal display device of avertical electric field mode, liquid crystal molecules are switched by avertical electric field which is produced between a pixel electrodeformed on an array substrate and a common electrode formed on acounter-substrate.

In the meantime, in the liquid crystal display device, an alignment filmis required in order to uniformize alignment directions of liquidcrystal molecules in a state in which no voltage is applied to a liquidcrystal layer. In general, an alignment film is formed by using anorganic material such as polyimide. In recent years, however, there hasbeen proposed a technique of forming the alignment film by an inorganicmaterial such as silicon dioxide (SiO₂).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view which schematically illustrates a structure and anequivalent circuit of a liquid crystal display panel LPN whichconstitutes a liquid crystal display device according to an embodiment.

FIG. 2 is a plan view which schematically illustrates a structureexample of one pixel PX of an array substrate AR which is applicable tothe liquid crystal display device of the embodiment.

FIG. 3 is a plan view which schematically illustrates a structureexample of one pixel PX of a counter-substrate CT which is applicable tothe liquid crystal display device of the embodiment.

FIG. 4 is a view which schematically illustrates a cross-sectionalstructure of the liquid crystal display panel LPN in an active areaincluding a switching element SW shown in FIG. 2.

FIG. 5 is a cross-sectional view which schematically illustrates across-sectional structure of an end portion of the liquid crystaldisplay panel LPN.

DETAILED DESCRIPTION

In general, according to one embodiment, a liquid crystal display deviceincludes: a first substrate including a first insulative substrate, aswitching element located above the first insulative substrate, a firstinterlayer insulation film covering the switching element, a firstcommon electrode formed on the first interlayer insulation film, asecond interlayer insulation film covering the first common electrode, apixel electrode formed on the second interlayer insulation film andelectrically connected to the switching element, and a first alignmentfilm covering the pixel electrode; a second substrate including a secondinsulative substrate, a second common electrode extending on that sideof the second insulative substrate, which is opposed to the firstsubstrate, and having the same potential as the first common electrode,and a second alignment film covering the second common electrode; asealant attaching the first substrate and the second substrate in astate in which a cell gap is created between the first substrate and thesecond substrate; and a liquid crystal layer including liquid crystalmolecules held between the first alignment film and the second alignmentfilm, wherein the first alignment film and the second alignment film areformed of a material in which a principal chain is composed of silica(SiO₂), and extend at a position overlapping the sealant between aninner face and an outer face of the sealant.

According to another embodiment, a liquid crystal display deviceincludes: a first substrate including a first insulative substrate, aswitching element located above the first insulative substrate, a firstinterlayer insulation film covering the switching element and includingan end face on an inside of a first substrate end portion of the firstinsulative substrate, a second interlayer insulation film covering theend face of the first interlayer insulation film and extending to thefirst substrate end portion, a pixel electrode formed on the secondinterlayer insulation film and electrically connected to the switchingelement, and a first alignment film covering the pixel electrode andextending to the first substrate end portion; a second substrateincluding a second insulative substrate, a second common electrodeextending on that side of the second insulative substrate, which isopposed to the first substrate, and a second alignment film covering thesecond common electrode and extending to a second substrate end portionof the second insulative substrate; a sealant which is in close contactwith the first alignment film and the second alignment film and attachesthe first substrate and the second substrate in a state in which a cellgap is created between the first substrate and the second substrate; anda liquid crystal layer including liquid crystal molecules held betweenthe first alignment film and the second alignment film, wherein thefirst alignment film and the second alignment film are formed of amaterial in which a principal chain is composed of silica (SiO₂).

Embodiments will now be described in detail with reference to theaccompanying drawings. In the drawings, structural elements having thesame or similar functions are denoted by like reference numerals, and anoverlapping description is omitted.

FIG. 1 is a view which schematically shows a structure and an equivalentcircuit of a liquid crystal display panel LPN which constitutes a liquidcrystal display device according to an embodiment.

Specifically, the liquid crystal display device includes anactive-matrix-type liquid crystal display panel LPN. The liquid crystaldisplay panel LPN is configured to include an array substrate AR whichis a first substrate, a counter-substrate CT which is a second substratethat is disposed to be opposed to the array substrate AR, and a liquidcrystal layer LQ which is held between the array substrate AR and thecounter-substrate CT. The liquid crystal display panel LPN includes anactive area ACT which displays an image. The active area ACT correspondsto a region where the liquid crystal layer LQ is held between the arraysubstrate AR and the counter-substrate CT, has a rectangular shape, forinstance, and is composed of a plurality of pixels PX which are arrayedin a matrix.

The array substrate AR includes, in the active area ACT, a plurality ofgate lines G (G1 to Gn) extending in a first direction X, a plurality ofsource lines S (S1 to Sm) extending in a second direction Y crossing thefirst direction X, a switching element SW which is electricallyconnected to the gate line G and source line S in each pixel PX, a pixelelectrode PE which is electrically connected to the switching element SWin each pixel PX, and a first common electrode CE1 which is opposed tothe pixel electrode PE. A storage capacitance CS is formed, for example,between the first common electrode CE1 and the pixel electrode PE.

On the other hand, the counter-substrate CT includes, for example, asecond common electrode CE2 which is opposed to the pixel electrode PEvia the liquid crystal layer LQ.

Each of the gate lines G is led out to the outside of the active areaACT and is connected to a first driving circuit GD. Each of the sourcelines S is led out to the outside of the active area ACT and isconnected to a second driving circuit SD. At least parts of the firstdriving circuit GD and second driving circuit SD are formed on, forexample, the array substrate AR, and are connected to a driving IC chip2. The driving IC chip 2 incorporates a controller which controls thefirst driving circuit GD and second driving circuit SD, and functions asa signal supply source for supplying necessary signals for driving theliquid crystal display panel LPN. In the example illustrated, thedriving IC chip 2 is mounted on the array substrate AR, on the outsideof the active area ACT of the liquid crystal display panel LPN.

The first common electrode CE1 and second common electrode CE2 have thesame potential, and each of them extends over substantially the entiretyof the active area ACT and is formed commonly over a plurality of pixelsPX. The first common electrode CE1 and second common electrode CE2 areled out to the outside of the active area ACT and are connected to apower supply module Vcom. The power supply module Vcom is formed, forexample, on the array substrate AR on the outside of the active areaACT, and is electrically connected to the first common electrode CE1 andalso electrically connected to the second common electrode CE2 via anelectrically conductive member (not shown). At the power supply moduleVcom, for example, a common potential is supplied to the first commonelectrode CE1 and second common electrode CE2.

FIG. 2 is a plan view which schematically shows a structure example ofone pixel PX of the array substrate AR which is applicable to the liquidcrystal display device of the embodiment.

The array substrate AR includes a gate line G1, a source line S1, asource line S2, a switching element SW, a first common electrode CE1,and a pixel electrode PE. In the example illustrated, as indicated by abroken line in FIG. 2, the pixel PX has a rectangular shape with a pairof short sides parallel to the first direction X, and a pair of longsides parallel to the second direction Y.

The gate line G1 extends linearly in the first direction X. The sourceline S1 and source line S2 are disposed with a distance in the firstdirection X, and extend linearly in the second direction Y,respectively. The length of the pixel PX in the first direction X issubstantially equal to the pitch of neighboring source lines in thefirst direction X. The length of the pixel PX in the second direction Yis substantially equal to the pitch of neighboring gate lines in thesecond direction Y.

In the pixel PX illustrated, the source line S1 is located at a leftside end portion, and is disposed to extend over a boundary between thepixel PX and a pixel neighboring on the left side. The source line S2 islocated at a right side end portion, and is disposed to extend over aboundary between the pixel PX and a pixel neighboring on the right side.The gate line G1 is disposed in a manner to cross a central portion ofthe pixel PX. In the present embodiment, as illustrated, there is nostorage capacitance line which crosses the pixel PX for forming astorage capacitance CS.

The switching element SW is composed of, for example, an n-channelthin-film transistor (TFT). Although a detailed illustration is omitted,the switching element SW includes a semiconductor layer of, e.g.polysilicon, a gate electrode connected to the gate line G1, a sourceelectrode which is connected to the source line S1 and is put in contactwith the semiconductor layer, and a drain electrode WD which is put incontact with the semiconductor layer.

As indicated by lower-right hatching lines in the Figure, the firstcommon electrode CE1 is disposed over substantially the entirety of thepixel PX, and further extends from the pixel PX beyond the source lineS1 and source line S2 in the first direction X and extends in the seconddirection Y. Specifically, the first common electrode CE1 is opposed tothe source line S1 and source line S2 and is formed continuously overpixels neighboring the pixel PX in the first direction X. In addition,the first common electrode CE1 is formed continuously over pixelsneighboring the pixel PX in the second direction Y. Furthermore,although not described in detail, the first common electrode CE1 isdisposed over substantially the entirety of the active area whichdisplays an image, and a part thereof is led out to the outside of theactive area and electrically connected to the power supply module, asdescribed above. It should be noted, however, that an opening OP forexposing the drain electrode WD is formed in the first common electrodeCE1.

In the meantime, the first common electrode CE1 may be formed such that,while the first common electrode CE1 is disposed over substantially theentirety of the pixel PX, the first common electrode CE1 madediscontinuous at an area overlapping the gate line G1, the first commonelectrode CE1 extends from the pixel PX over the source line S1 andsource line S2 in the first direction X, the first common electrode CE1is opposed to the source line S1 and source line S2, and the firstcommon electrode CE1 is continuously formed in a strip shape over pixelsneighboring the pixel PX in the first direction X. In this case, too,the first common electrode CE1 is led out to the outside of the activearea which displays an image, and is electrically connected to the powersupply module, as described above.

As indicated by upper-right hatching lines in the Figure, the pixelelectrode PE is formed in an island shape in the pixel PX, and isopposed to the first common electrode CE1. Incidentally, in the exampleillustrated, although only the pixel electrode PE disposed in the pixelPX is depicted, pixel electrodes are also disposed in other pixelsneighboring the pixel PX in the first direction X and second directionY. The pixel electrode PE is electrically connected to the drainelectrode WD of the switching element SW via a contact hole CH. Theshape of the pixel electrode PE illustrated corresponds to, for example,the shape of the pixel PX, and is a rectangular shape having a lesslength in the first direction X than in the second direction Y. Thecontact hole CH is located at a substantially central part of the pixelelectrode PE. Incidentally, a part of the pixel electrode PE may extendto positions overlapping the source line S1 and source line S2.

In the present embodiment, the structure of each pixel of the activearea is identical to the above-described structure example. However, theactive area may include pixels of different pixel sizes, i.e. differentlengths in the first direction X and second direction Y.

FIG. 3 is a plan view which schematically shows a structure example ofone pixel PX of the counter-substrate CT which is applicable to theliquid crystal display device of the embodiment. FIG. 3 shows onlystructural parts that are necessary for the description, and the sourceline S1, source line S2, gate line G1, and pixel electrode PE, which aremain parts of the array substrate, are indicated by broken lines, andthe depiction of the first common electrode is omitted.

The counter-substrate CT includes a second common electrode CE2. Thesecond common electrode CE2 is disposed in the pixel PX, and is opposedto the pixel electrode PE. In addition, the second co mon electrode CE2extends from the pixel PX in the first direction X and the seconddirection Y, and is located also above the source line S1 and sourceline S2. Specifically, although not described in detail, the secondcommon electrode CE2 is disposed continuously over pixels neighboring onthe right side and left side along the first direction X of the pixelPX, and pixels neighboring on the upper side and lower side along thesecond direction Y of the pixel PX. Furthermore, although not describedin detail, the second common electrode CE2 is disposed oversubstantially the entirety of the active area.

A slit SL is formed in the second common electrode CE2 at a positionopposed to the pixel electrode PE. In the example illustrated, the slitSL is formed in a strip shape extending in the second direction Y, andis located substantially at a central part of the pixel PX. This slit SLcorresponds to an alignment control member which mainly controls thealignment of liquid crystal molecules. In the meantime, instead of theslit, some other alignment control member, such as a projection stackedon the second common electrode CE2, may be disposed, if such analignment control member has a function of controlling the alignment ofliquid crystal molecules. In addition, the shape of the slit SL is notlimited to the example illustrated, and may be, for instance, a crossshape.

FIG. 4 is a view which schematically illustrates a cross-sectionalstructure of the liquid crystal display panel LPN in the active areaincluding the switching element SW shown FIG. 2.

The array substrate AR is formed by using a first insulative substrate10 having light transmissivity, such as a glass substrate or a resinsubstrate. The array substrate AR includes, on that side of the firstinsulative substrate 10, which is opposed to the counter-substrate CT, aswitching element SW, a first common electrode CE1, a pixel electrodePE, a first insulation film 11, a second insulation film 12, a thirdinsulation film 13, a fourth insulation film 14, and a first alignmentfilm AL1.

In the example illustrated, the switching element SW is a thin-filmtransistor of a top gate type. The switching element SW includes asemiconductor layer SC which is disposed on the first insulativesubstrate 10. In the meantime, an undercoat layer, which is aninsulation film, may be interposed between the first insulativesubstrate 10 and the semiconductor layer SC. The semiconductor layer SCis covered with the first insulation film 11. The first insulation film11 is also disposed on the first insulative substrate 10. This firstinsulation film 11 is formed of, for example, an inorganic material suchas silicon nitride.

A gate electrode WG of the switching element SW is formed on the firstinsulation film 11, and is located immediately above the semiconductorlayer SC. The gate electrode WG is electrically connected to the gateline G1 (or formed integral with the gate line G1) and is covered withthe second insulation film 12. The second insulation film 12 is alsodisposed on the first insulation film 11. This second insulation film 12is formed of, for example, an inorganic material such astetraethoxysilane (TEOS).

A source electrode WS and a drain electrode WD of the switching elementSW are formed on the second insulation film 12. The source line S1 andsource line S2 are similarly formed on the second insulation film 12.The source electrode WS illustrated is electrically connected to thesource line S1 (or formed integral with the source line S1). The sourceelectrode WS and drain electrode WD are put in contact with thesemiconductor layer SC via contact holes penetrating the firstinsulation film 11 and second insulation film 12. The switching elementSW with this structure, as well as the source line S1 and source lineS2, is covered with the third insulation film 13. The third insulationfilm 13 is also disposed on the second insulation film 12. This thirdinsulation film 13 is formed of, for example, a transparent resinmaterial.

This third insulation film 13 corresponds to a first interlayerinsulation film which covers the source line S1, source line S2 andswitching element SW.

The first common electrode CE1 extends over the third insulation film13. As illustrated in the Figure, the first common electrode CE1 coversthe upper side of the source line S1 and source line S2, and extendstoward neighboring pixels. The first common electrode CE1 is formed of atransparent, electrically conductive material such as indium tin oxide(ITO) or indium sine oxide (IZO). The fourth insulation film 14 isdisposed on the first common electrode CE1. A contact hole CH, whichpenetrates to the drain electrode WD, is formed in the third insulationfilm 13 and fourth insulation film 14. The fourth insulation film 14 hasa less thickness than the third insulation film 13, and is formed of,for example, an inorganic material such as silicon nitride.

This fourth insulation film 14 corresponds to a second interlayerinsulation film which covers the first common electrode CE1.

The pixel electrode PE is formed in an island shape on the fourthinsulation film 14 and is opposed to the first common electrode CE1. Thepixel electrode PE is electrically connected to the drain electrode WDof the switching element SW via the contact hole CH. This pixelelectrode PE is formed of a transparent, electrically conductivematerial such as ITO or IZO. The pixel electrode PE is covered with thefirst alignment film AL1.

On the other hand, the counter-substrate CT is formed by using a secondinsulative substrate 30 with light transmissivity, such as a glasssubstrate or a resin substrate. The counter-substrate CT includes, onthat side of the second insulative substrate 30, which is opposed to thearray substrate AR, a light-shield layer 31, color filters 32, anovercoat layer 33, a second common electrode CE2, and a second alignmentfilm AL2.

The light-shield layer 31 partitions each pixel PX in the active areaACT, and forms an aperture portion AP. The light-shield layer 31 isprovided at boundaries between color pixels, or at positions opposed tothe source lines provided on the array substrate AR and positionsopposed to the switching elements provided on the array substrate AR.The light-shield layer 31 is formed of a light-shielding metallicmaterial or a black resin material.

The color filter 32 is formed in the aperture portion AP, and a partthereof overlaps the light-shield layer 31. The color filters 32include, for example, a red color filter formed of a resin materialwhich is colored in red, a green color filter formed of a resin materialwhich is colored in green, and a blue color filter formed of a resinmaterial which is colored in blue. The red color filter is disposed in ared pixel which displays red, the green color filter is disposed in agreen pixel which displays green, and the blue color filter is disposedin a blue pixel which displays blue. In addition, a white (ortransparent) color filter is disposed in a white pixel which displayswhite. Incidentally, no color filter may be disposed in the white pixel.Besides, the white color filter may not strictly be an achromatic colorfilter, and may be a color filter which is lightly colored (e.g. coloredin light yellow). Boundaries between the color filters 32 of differentcolors are located at positions overlapping the light-shield layer 31above the source lines S.

The overcoat layer 33 covers the color filters 32. The overcoat layer 33planarizes asperities of the light-shield layer 31 and color filters 32.The overcoat layer 33 is formed of, for example, a transparent resinmaterial. This overcoat layer 33 serves as an underlayer of the secondcommon electrode CE2.

The second common electrode CE2 is formed on that side of the overcoatlayer 33, which is opposed to the array substrate AR. As illustrated inthe Figure, the second common electrode CE2 extends above the sourceline S1 and source line S2, and extends toward the neighboring pixels.The second common electrode CE2 is formed of, for example, atransparent, electrically conductive material such as ITO or IZO. Thesecond common electrode CE2 is covered with the second alignment filmAL2.

The first alignment film AL1 and second alignment film AL2 are formed ofa material which exhibits vertical alignment properties, and have analignment restriction force which aligns liquid crystal molecules in anormal direction of the array substrate AR or counter-substrate CT,without requiring alignment treatment such as rubbing.

In the present embodiment, the first alignment film AL1 and secondalignment film AL2 are formed of a material in which a principal chainis composed of silica (SiO₂).

The above-described array substrate AR and counter-substrate CT aredisposed such that their first alignment film AL1 and second alignmentfilm AL2 are opposed to each other. In this case, a predetermined cellgap is created between the array substrate AR and the counter-substrateCT by columnar spacers which are formed on one of the array substrate ARand counter-substrate CT. The array substrate AR and counter-substrateCT are attached by a sealant in the state in which the cell gap iscreated. The liquid crystal layer LQ is sealed between the firstalignment film AL1 and second alignment film AL2. This liquid crystallayer LQ is composed of a liquid crystal composition with a negative(negative-type) dielectric constant anisotropy.

A backlight unit BL is disposed on the back side of the liquid crystaldisplay panel LPN having the above-described structure. Various modesare applicable to the backlight unit BL, but a description of thedetailed structure of the backlight unit BL is omitted here.

A first optical element OD1 including a first polarizer PL1 is disposedon an outer surface 10B of the first insulative substrate 10. A secondoptical element OD2 including a second polarizer PL2 is disposed on anouter surface 30B of the second insulative substrate 30. The firstpolarizer PL1 and second polarizer PL2 are disposed, for example, in apositional relationship of crossed Nicols in which their polarizationaxes are perpendicular to each other.

FIG. 5 is a cross-sectional view which schematically illustrates across-sectional structure of an end portion of the liquid crystaldisplay panel LPN.

Specifically, in the array substrate AR, the first insulation film 11and second insulation film 12 extend to a substrate end portion 10E ofthe first insulative substrate 10. The third insulation film 13 has anend face 13E on the inside of the substrate end portion 10E. The fourthinsulation film 14 is disposed in a manner to cover the end face 13E,extends further to the outside, and extends to the substrate end portion10E. In the vicinity of the substrate end portion 10E, the fourthinsulation film 14 overlaps the second insulation film 12. The firstalignment film AL1 is disposed on the fourth insulation film 14, andcontinuously extends to the substrate end portion 10E. Specifically, theentirety of the first alignment film AL1 is stacked on the fourthinsulation film 14.

On the other hand, in the counter-substrate CT, the light-shield layer31 extends to a substrate end portion 30E of the second insulativesubstrate 30. The color filter 32 has an end face 32E on the inside ofthe substrate end portion 30E. The overcoat layer 33 is formeddiscontinuous on the inside of the substrate end portion 30E.Specifically, in the overcoat layer 33, a groove 33G reaching thelight-shield layer 31 is formed between a segment 331 which extends tothe substrate end portion 30E and a segment 332 which is located insidethe substrate end portion 30E. The second alignment film AL2 is disposedin a manner to cover the overcoat layer 33, and continuously extends tothe substrate end portion 30E. Specifically, the second alignment FilmAL2 covers the segment 331 and segment 332, and is also filled in thegroove 33G.

The array substrate AR and counter-substrate CT are attached by asealant SE. The sealant SE illustrated includes an inner face SEI whichis in contact with the liquid crystal layer LQ, and an outer face SEOwhich is located on the side of the substrate end portion 10E andsubstrate end portion 30E. The width of the sealant SE corresponds to adistance from the inner face SEI to the outer face SEO in a directionparallel to the substrate major surface.

If attention is paid to the positional relationship between this sealantSE and the first alignment film AL1 and second alignment film AL2, thefirst alignment film AL1 and second alignment film AL2 extend at aposition overlapping the sealant SE between the inner face SEI and outerface SEO of the sealant SE. Specifically, the first alignment film AL1and second alignment film AL2 overlap the sealant SE over the entirewidth of the sealant SE. Each of an end face AE1 of the first alignmentfilm AL1 and an end face AE2 of the second alignment film AL2 is exposedfrom the sealant SE. Incidentally, in the array substrate AR, therespective end faces of the first insulation film 11, second insulationfilm 12 and fourth insulation film 14 are exposed from the sealant SE atthe substrate end portion 10E. Similarly, in the counter-substrate CT,the respective end faces of the light-shield layer 31 and segment 331are exposed from the sealant SE at the substrate end portion 30E.

The first alignment film AL1 lies between the fourth insulation film 14and the sealant SE. Specifically, the entirety of the lower surface ofthe sealant SE on the array substrate side is an close contact with thefirst alignment film AL1. The second alignment film AL2 lies between theovercoat layer 33 and the sealant SE. Specifically, the entirety of theupper surface of the sealant SE on the counter-substrate side is inclose contact with the second alignment film AL2. These first alignmentfilm AL1 and second alignment film AL2 are formed of the material inwhich the principal chain is composed of silica (SiO₂), as describedabove, and are strongly bonded to the sealant SE by covalent bond.

Next, an example of the operation of the liquid crystal display devicein the embodiment is described.

In an OFF state in which no potential difference is produced between thepixel electrode PE and the second common electrode CE2 (i.e. a state inwhich no voltage is applied to the liquid crystal layer LQ), no electricfield is produced between the pixel electrode PE and second commonelectrode CE2. Thus, as illustrated in FIG. 4, liquid crystal moleculesLM included in the liquid crystal layer LQ are initially alignedsubstantially perpendicular to the substrate major surface (X-Y plane)between the first alignment film AL1 and second alignment film AL2. Atthis time, part of linearly polarized light from the backlight unit ELpasses through the first polarizer PL1 and enters the liquid crystaldisplay panel LPN. The polarization state of the linearly polarizedlight, which enters the liquid crystal display panel LPN, hardly varieswhen the light passes through the liquid crystal layer LQ. Thus, thelinearly polarized light emerging from the liquid crystal display panelLPN is absorbed by the second polarizer PL2 that is in the positionalrelationship of crossed Nicols in relation to the first polarizer PL1(black display).

In an ON state in which a potential difference is produced between thepixel electrode PE and the second common electrode CE2 (i.e. a state inwhich a voltage is applied to the liquid crystal layer LQ), a verticalelectric field or an inclined electric field avoiding the slit SL isproduced between the pixel electrode PE and second common electrode CE2.Thus, the liquid crystal molecules LM are aligned in a directiondifferent from the vertical alignment direction, by the effect of thevertical electric field or inclined electric field. Specifically, sincenegative-type liquid crystal molecules LM are aligned such that theirmajor axes cross the electric field, the liquid crystal molecules LM arealigned in the ON state in an oblique direction or in a horizontaldirection, relative to the substrate major surface.

In this ON state, the polarization state of the linearly polarizedlight, which enters the liquid crystal display panel LPN, variesdepending on the alignment state of the liquid crystal molecules LM (orthe retardation of the liquid crystal layer) when the light passesthrough the liquid crystal layer LQ. Thus, in the ON state, at leastpart of the light emerging from the liquid crystal layer LQ passesthrough the second polarizer PL2 (white display).

In addition, in the ON state, a storage capacitance CS is formed by thepixel electrode PE and the first common electrode CE1 that are opposedto each other via the fourth insulation film 14, and retains a necessarycapacitance for displaying an image. Specifically, a pixel potential,which has been written in each pixel via the switching element SW, isretained in the storage capacitance CS for a predetermined period.

According to the present embodiment, the first alignment film AL1 andsecond alignment film AL2 are formed not of an organic material such aspolyimide, but of an inorganic material in which a principal chain iscomposed of silica (SiO₂). In addition, the first alignment film AL1 andsecond alignment film AL2 extend at a position overlapping the sealantSE between the inner face SEI and outer face SEO of the sealant SE.Thus, regardless of the layer structures at end portions overlapping thesealant SE in the array substrate AR and counter-substrate CT, the firstalignment film AL1 is located at an interface between the arraysubstrate AR and sealant SE, and the second alignment film AL2 islocated at an interface between the counter-substrate CT and sealant SE.Since the first alignment film AL1 and second alignment film AL2 arestrongly bonded to the sealant SE by covalent bond, the strength ofadhesion to the sealant SE can be improved. Therefore, it is possible tosuppress peeling between the array substrate AR and counter substrate CTin the liquid crystal display panel LPN.

The inventor prepared a liquid crystal display panel which has beendescribed in the embodiment, and a liquid crystal display panel of acomparative example, and measured the force (strength of adhesion) thatis necessary for peeling between the array substrate AR andcounter-substrate CT with respect to the respective liquid crystaldisplay panels. In the liquid crystal display panel of the comparativeexample, both the first alignment film AL1 and second alignment film AL2were formed of polyimide, and the same structure as in the presentembodiment was adopted. According to the liquid crystal display panel ofthe present embodiment, a strength of adhesion, which is about threetimes higher than the liquid crystal display panel of the comparativeexample, was obtained. The reason for this is that in the liquid crystaldisplay panel of the comparative example, the sealant SE is ionic-bondedto the first alignment film AL1 and second alignment film AL2, whereasin the liquid crystal display panel of the present embodiment, thesealant SE is covalent-bonded to the first alignment film AL1 and secondalignment film AL2.

In addition, according to the present embodiment, each of the firstalignment film AL1 and second alignment film AL2 extends at a positionoverlapping the sealant SE, and each end face thereof is exposed fromthe sealant. However, since the first alignment film AL1 and secondalignment film AL2 are formed of the inorganic material, the moistureabsorption is very small, compared to the organic material.

Furthermore, in the array substrate AR, the third insulation film 13,which is formed of the organic material, has the end face 13E on theinside of the substrate end portion 10E, and this end face 13E iscovered with the fourth insulation film 14 and first alignment film AL1which are formed of the inorganic material. Thus, there is no path ofmoisture entering the third insulation film 13 from the outside. Inaddition, in the counter-substrate CT, although the segment 331 or theovercoat layer 33 is exposed on the substrate end portion 30E side, thesegment 331 is separated from the segment 332 which is located on theinner side, and this overcoat layer 33 is covered with the secondalignment film AL2. Thus, a path of moisture entering the overcoat layer33 from the outside is made discontinuous between the segment 331 andsegment 332. Thereby, it becomes possible to suppress damage to theliquid crystal display panel LPN due to moisture.

The inventor prepared a liquid crystal display panel which has beendescribed in the embodiment, and a liquid crystal display panel of acomparative example, and conducted an operation test for displaying animage, after each liquid display panel was left for 500 hours in ahigh-temperature, high-humidity environment (temperature: 60° C.,humidity: 95%). The structure of the liquid crystal display panel of thecomparative example is as described above. As regards the liquid crystaldisplay panel of the comparative example, a display defect was confirmedwhen an image was displayed. However, as regards the liquid crystaldisplay panel of the present embodiment, no display defect was confirmedwhen an image was displayed.

Therefore, according to the present embodiment, the reliability can beenhanced.

Furthermore, according to the embodiment, the capacitance, which isnecessary for displaying an image in each pixel, can be formed by the pelectrode PE and first common electrode CE1 which are opposed via thefourth insulation film 14. Thus, when the capacitance is formed, awiring line or electrode, which crosses the pixel and is formed of alight-shielding wiring material, is needless. In addition, the fourthinsulation film 14 is formed to have a smaller film thickness than thethird insulation film that is formed of a resin material or the like.Therefore, a relatively large capacitance can easily be formed by thepixel electrode PE and first common electrode CE1 which are disposed viathe fourth insulation film 14.

Moreover, since each of the pixel electrode PE and first commonelectrode CE1 is formed of a transparent, electrically conductivematerial, an area overlapping the pixel electrode PE and first commonelectrode CE1 contributes to display. Thus, compared to a comparativeexample in which a storage capacitance line crossing the pixel isdisposed, the aperture ratio which contributes to display, transmittanceor luminance per pixel, can be improved. Therefore, while thecapacitance necessary for display is secured, the display quality can beimproved.

In addition, the first common electrode CE1 extends above the sourceline S1 and source line S2. Thus, in the ON state, an undesired leakelectric field from the source line toward the liquid crystal layer LQcan be shielded by the first common electrode CE1. Specifically, it ispossible to suppress formation of an undesired electric field or anundesired capacitance between the source line and the pixel electrode PEor second common electrode CE2, and to suppress disturbance in alignmentof liquid crystal molecules LM in an area overlapping the source line.

Furthermore, the liquid crystal molecules LM in the area overlapping thesource line maintains the initial alignment state even in the ON state,since the first common electrode CE1 and second common electrode CE2 arekept at the same potential. Therefore, pixel electrodes PE neighboringin the first direction X can be located closer to each other up to aprocessing limit, and the area which contributes to display per pixelcan further be increased.

Besides, even when one of the pixels neighboring with the source lineinterposed is in the ON state and the other is in the OFF state, thereis no potential difference, by the first common electrode CE1 and secondcommon electrode CE2, in the liquid crystal layer on the source linebetween the ON-state pixel and OFF-state pixel. Thus, the liquid crystalmolecules LM in the area overlapping the source line are kept in theinitial alignment state. Therefore, even when the liquid crystal displaypanel LPN is viewed in an oblique direction, degradation in displayquality due to color mixing can be suppressed. In addition, since thereis no need to increase the width of the light-shield layer 31 in orderto prevent color mixing, the area contributing to display per pixel canfurther be increased.

As has been described above, according to the present embodiment, aliquid crystal display device, which can enhance reliability, can beprovided.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the inventions. Indeed, the novel embodiments described hereinmay be embodied in a variety of other forms; furthermore, variousomissions, substitutions and changes in the form of the embodimentsdescribed herein may be made without departing from the spirit of theinventions. The accompanying claims and their equivalents are intendedto cover such forms or modifications as would fall within the scope andspirit of the inventions.

What is claimed is:
 1. A liquid crystal display device comprising: anarray substrate including an insulative substrate, a first film, asecond film on the first film, a third film on the second film, a fourthfilm on the third film, a common electrode, and pixel electrodes; acounter substrate; a sealant attaching the array substrate and thecounter substrate in a seal region; and a liquid crystal layer heldbetween the array substrate and the counter substrate on an inside ofthe sealant, wherein the first film is between the insulative substrateand the second film, the second film is between the first film and thethird film, the third film is between the second film and the fourthfilm, the fourth film is between the third film and sealant, the commonelectrode is between the second film and the liquid crystal layer, thepixel electrodes are between the second film and the liquid crystallayer, the second film includes an end face in the seal region, in aregion between an end portion of the insulative substrate and the endface of the second film, the first film is exposed from the second film,in the seal region, the fourth film is disposed to cover the end face ofthe second film, in the seal region, a part of the third film issandwiched between the fourth film and the end face of the second film,and the second film is formed of an organic material.
 2. The liquidcrystal display device of claim 1, wherein the first film is formed ofan inorganic material, the third film is formed of an inorganicmaterial, and the fourth film is formed of an inorganic material.
 3. Theliquid crystal display device of claim 2, wherein the common electrodeis between the second film and the third film.
 4. The liquid crystaldisplay device of claim 3, wherein the pixel electrodes are between thethird film and the fourth film.
 5. The liquid crystal display device ofclaim 2, wherein, in the region between the end portion of theinsulative substrate and the end face of the second film, the third filmis in contact with the first film.
 6. The liquid crystal display deviceof claim 5, wherein, in the region between the end portion of theinsulative substrate and the end face of the second film, the fourthfilm covers the third film.
 7. The liquid crystal display device ofclaim 6, wherein, in the region between the end portion of theinsulative substrate and the end face of the second film, the sealant isin contact with the fourth film.
 8. The liquid crystal display device ofclaim 7, wherein the fourth film is an alignment film.
 9. The liquidcrystal display device of claim 7, wherein an end face of the fourthfilm is exposed from the sealant.
 10. The liquid crystal display deviceof claim 7, wherein the counter substrate includes an overcoat layer andthe light-shield layer, the overcoat layer is between the light-shieldlayer and the liquid crystal layer, and in the seal region, the overcoatlayer includes a groove reaching the light-shield layer.
 11. The liquidcrystal display device of claim 10, wherein the sealant includes aninner face facing the liquid crystal layer, the groove of the overcoatlayer is between the inner face of the sealant and the end face of thesecond film.